How do I move a light to another room in my Philips Hue app?

Go to the 'Settings' > 'Room setup' and tap the room where you want to add or remove a light. It will display all the lights which are connected to your Hue system. The lights which have a check mark are part of the room (p.s. beneath the light names you can see to which room the light connected to). By unchecking or checking the box you can add or remove lights from your room.